The present invention relates to systems designed to remove pollutants from the air including both particulates and gaseous contaminants. In many industrial operations a considerable quantity of contaminants are produced which must be removed from the air before it can be discharged to the atmosphere. This is particularly true in the case of mining operations where considerable dust is produced in the form of very small particulate matter.
In the past, it has been the practice to use wet scrubbers for removing the particulate matter from the air because of their low capital cost and their ability to remove both the particulate and gaseous contaminants. While wet scrubbers are in wide use, they have a major drawback in that their operation requires considerable energy. The conventional wet scrubber consists of pressure nozzles that produce droplets in the size range of several hundred microns that are ineffective in capturing the respirable-size particulates contained in normal contaminants. It has been the customary practice to use a venturi section in a duct to create sufficient velocity of air flow to break up the large droplets in the scrubbing liquid into small droplets in the range of from 5 to 100 microns. While the use of a venturi section effectively breaks up the large droplets to provide the 5 to 100 micron size droplets required for removing respirable-size particles from the air, it is a very inefficient means for producing the required droplet size. This inefficiency results in an increased cost of operation of the system. The pressure differential over the scrubber length for a conventional wet scrubber is 10 to 100 inches of water column while the pressure differential for the device of the present invention is 5 to 10 inches of water column. From this comparison it is seen that the major energy consumption is in scrubber water atomization.
Another drawback of using wet scrubbers is freezing of the scrubbing water during severe cold weather. Small drops can be quickly frozen as they encounter the cold air, rendering them ineffective in capturing the dust particles. Therefore, wet scrubbers are rarely used in cold regions.
Another method that is in common use for removing particulate matter from air streams is the conventional baghouse in which cloth filters are used to remove the particulate matter from the flowing air stream. While the baghouse is an effective means for removing the respirable size particles from the air stream, it is expensive to install and requires considerable maintenance during operation. The air flow must be reversed periodically to remove the particulate matter which is collected on the individual filters to maintain the air flow through the baghouse. Likewise, provisions must be provided for periodically removing the particulate matter which is collected in the baghouse. This can involve the expenditure of considerable money and time. In order to perform the various maintenance functions on the baghouse, it is necessary to shut down the baghouse temporarily while the maintenance is being performed. If it is desired to maintain continuous operation, this necessitates the installation of sufficient baghouses so that operations can be maintained while a certain percentage of the baghouses are shut down for routine maintenance.
In many installations, the particulate matter filling the baghouse can form an explosive mixture. This is especially true in the case of coal dust or dust from food grains.